Instrumental Evaluation of Thin-Layer Chromatograms

Abstract

Recent changes in the practice of thin-layer chromatography (TLC) have created a renaissance of interest in this technique and led to its wider acceptance as a powerful tool for qualitative and quantitative analysis of mixtures. The performance breakthrough in TLC, referred to as high performance thin-layer chromatography (HPTLC), was not a result of any specific advances in instrumentation or materials, but was rather a culmination of improvements in practically all of the operations comprising TLC, [1–6]. Improvements in the quality of the sorbent layer, methods of sample application, new development techniques, and the availability of scanning densitometers for in situ quantitative analysis were all important developments in the evolution of HPTLC. The new HPTLC plates were prepared from sorbents of smaller average particle diameter and of narrower particle size distribution than those used to prepare conventional TLC plates. The performance of these plates improved an order of magnitude over those used for conventional TLC. Because of the lower sample capacity of the HPTLC sorbent layer, the amount of sample applied to it had to be scaled down from those commonly used in conventional TLC. Typical sample volumes applied to the plates are in the range 100–200 nl, sample amounts less than ca. 0.1 μg, and starting spot sizes of 1.0–2.0 mm.